RBTree delegates and types

[Steven Schveighoffer]

On 3/18/18 8:34 AM, Viktor wrote:
> Hey,
> 
> I'm trying to convert an old legacy app to D and have a couple of 
> questions. It has been a very fun weekend!
> 
> First, I could not make std.container.rbtree use a delegate for a 
> comparator. The docs say it should be possible, but I got a weird error.
> 
> I tracked it down to RedBlackTreee.opEquals() using explicit function 
> when calling equals():
> 
> return equal!(function(Elem a, Elem b) => !_less(a,b) && 
> !_less(b,a))(thisRange, thatRange);
> 
> When I removed the "function" things started compiling (I have yet to 
> test the code due to question #2 below). I've done a dub -b unittest 
> without issues so it might be OK.
> 
> So, the first...several questions are: do you think this change is safe 
> and should I raise an issue in the bugzilla or do a PR for it on github? 

Yes, seems like an oversight. RedBlackTree.opEquals was added almost 6 
years ago, and it's possible this wouldn't have worked back then 
(https://github.com/dlang/phobos/pull/900)


> Should it include a new unittest that makes sure rbtree can be 
> instantiated with a delegate?

Definitely. Thanks for thinking of this!

> 
> The other part I'm still struggling with is about auto types. Can I 
> store the rbtree type in the following class so it can be used from 
> another method?
> 
> class Indexer(T, alias pred)
> {
       alias RBType = RedBlackTree!(uint, (a, b) => comp(a, b));
>     this(T storage)
>     {
>        this.storage = storage;

          this.index = new RBType();

>     }

> 
>     void dumpIndex()
>     {
>         // how to get my dirty hands on the index here?

           // answer: just use it?

>     }
> 
>     bool comp(uint i1, uint i2)
>     {
>        auto rec1 = storage[i1];
>        auto rec2 = storage[i2];
>        return pred(rec1, rec2);
>     }
> 
>     private T storage;

       RBType index;

> }
> 

-Steve